<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<meta name="viewport" content="initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
		<title>丝带旋转动画</title>
		<style type="text/css">
			body {
  background: #d1684e;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  -webkit-touch-callout: none;
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
}

#wrap {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  overflow: hidden;
}

#wrap canvas {
  position: absolute;
  left: 50%;
  top: 50%;
  width: 500px;
  height: 500px;
  margin: -250px 0 0 -250px;
  -outline: 1px solid #fff;
}

.info {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  font-size: 12px;
  color: #ccc;
  line-height: 2em;
  text-align: center;
  font-family: "微软雅黑";
}
		</style>
	</head>
	<body>
		<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r77/three.min.js"></script>
<div id="wrap"></div>
<p class="info">一直按住鼠标左键查看效果</p>


<script type="text/javascript">
	var $body = document.body,
  $wrap = document.getElementById('wrap'),

  areawidth = window.innerWidth,
  areaheight = window.innerHeight,

  canvassize = 500,

  length = 30,
  radius = 5.6,

  rotatevalue = 0.035,
  acceleration = 0,
  animatestep = 0,
  toend = false,

  pi2 = Math.PI * 2,

  group = new THREE.Group(),
  mesh, ringcover, ring,

  camera, scene, renderer;

camera = new THREE.PerspectiveCamera(65, 1, 1, 10000);
camera.position.z = 150;

scene = new THREE.Scene();
// scene.add(new THREE.AxisHelper(30));
scene.add(group);

mesh = new THREE.Mesh(
  new THREE.TubeGeometry(new(THREE.Curve.create(function() {},
    function(percent) {

      var x = length * Math.sin(pi2 * percent),
        y = radius * Math.cos(pi2 * 3 * percent),
        z, t;

      t = percent % 0.25 / 0.25;
      t = percent % 0.25 - (2 * (1 - t) * t * -0.0185 + t * t * 0.25);
      if (Math.floor(percent / 0.25) == 0 || Math.floor(percent / 0.25) == 2) {
        t *= -1;
      }
      z = radius * Math.sin(pi2 * 2 * (percent - t));

      return new THREE.Vector3(x, y, z);

    }
  ))(), 200, 1.1, 2, true),
  new THREE.MeshBasicMaterial({
    color: 0xffffff
      // , wireframe: true
  })
);
group.add(mesh);

ringcover = new THREE.Mesh(new THREE.PlaneGeometry(50, 15, 1), new THREE.MeshBasicMaterial({
  color: 0xd1684e,
  opacity: 0,
  transparent: true
}));
ringcover.position.x = length + 1;
ringcover.rotation.y = Math.PI / 2;
group.add(ringcover);

ring = new THREE.Mesh(new THREE.RingGeometry(4.3, 5.55, 32), new THREE.MeshBasicMaterial({
  color: 0xffffff,
  opacity: 0,
  transparent: true
}));
ring.position.x = length + 1.1;
ring.rotation.y = Math.PI / 2;
group.add(ring);

// fake shadow
(function() {
  var plain, i;
  for (i = 0; i < 10; i++) {
    plain = new THREE.Mesh(new THREE.PlaneGeometry(length * 2 + 1, radius * 3, 1), new THREE.MeshBasicMaterial({
      color: 0xd1684e,
      transparent: true,
      opacity: 0.13
    }));
    plain.position.z = -2.5 + i * 0.5;
    group.add(plain);
  }
})();

renderer = new THREE.WebGLRenderer({
  antialias: true
});
renderer.setPixelRatio(window.devicePixelRatio);
renderer.setSize(canvassize, canvassize);
renderer.setClearColor('#d1684e');

$wrap.appendChild(renderer.domElement);

$body.addEventListener('mousedown', start, false);
$body.addEventListener('touchstart', start, false);
$body.addEventListener('mouseup', back, false);
$body.addEventListener('touchend', back, false);

animate();

function start() {
  toend = true;
}

function back() {
  toend = false;
}

function tilt(percent) {
  group.rotation.y = percent * 0.5;
}

function render() {

  var progress;

  animatestep = Math.max(0, Math.min(240, toend ? animatestep + 1 : animatestep - 4));
  acceleration = easing(animatestep, 0, 1, 240);

  if (acceleration > 0.35) {
    progress = (acceleration - 0.35) / 0.65;
    group.rotation.y = -Math.PI / 2 * progress;
    group.position.z = 50 * progress;
    progress = Math.max(0, (acceleration - 0.97) / 0.03);
    mesh.material.opacity = 1 - progress;
    ringcover.material.opacity = ring.material.opacity = progress;
    ring.scale.x = ring.scale.y = 0.9 + 0.1 * progress;
  }

  renderer.render(scene, camera);

}

function animate() {
  mesh.rotation.x += rotatevalue + acceleration;
  render();
  requestAnimationFrame(animate);
}

function easing(t, b, c, d) {
  if ((t /= d / 2) < 1) return c / 2 * t * t + b;
  return c / 2 * ((t -= 2) * t * t + 2) + b;
}
</script>
	</body>
</html>
